Convection in water-alcohol mixtures differs substantially from that in pure fluids due to the additional time scale associated with the concentration field and the coupling between the temperature field and the alcohol concentration through the Soret effect (the alcohol concentration is enhanced in the regions of higher temperature). Specifically, convection can occur in an oscillatory fashion leading to traveling waves.
Numerical simulations of extended traveling waves by the group of M. Luecke (Phys. Rev. E 51 (1995) 5636):
In experiments also localized traveling waves have been observed by a number of groups (e.g. Kolodner (Phys. Rev. E 50 (1994) 2731)). Below is shown a top view of an annular cell. Convection is visualized by the shadowgraph method (i.e. cold sinking fluid is bright).
The detailed structure of the convective flow is revealed in the numerical simulations by the group of M. Luecke (Phys. Rev. E 51 (1995) 5662). The picture shows a lateral view of a convection cell. The top portion shows a localized wave, which is compared with the extended wave in the bottom part.
The slow dynamics of the concentration field becomes apparent in its much slower spatial decay compared to that of the convective amplitude (most notably at the left end of the localized wave puls). In weakly nonlinear descriptions this necessitates the inclusion of an additional field in addition to the convective amplitude (H. Riecke, Phys. Rev. Lett. 68 (1992) 301). The figure below shows a localized wave pulse within such a weakly nonlinear theory.
